Formulation of 3D Soil Springs for Pipe Stress Analyses

Interdependence between pipe-soil interaction springs in a pipe stress analysis should be considered. This example focused on a single pipe configuration “wished” in place in a clay soil. A conventional pipe stress analyses often idealizes the pipe soil interaction with a beam-spring finite element model where independence is assumed between reactions in axial, lateral and vertical directions. There is however interdependence between these springs as recognized in recent Pipeline Research Council International (PRCI) guidelines. For a frictional interface, axial resistance can be much higher than indicated by PRCI guidelines when accounting for increased lateral and vertical bearing pressure. At the same time, lateral and vertical capacities are shown to be reduced in comparison to pure vertical and lateral loading directions. This paper highlights the development of a 3D soil-spring interaction model based on a continuum finite element analysis approach. By developing a soil capacity envelope based on 3D continuum modeling, updated soil springs can reflect modified capacities depending on the direction of pipe movement. For the landslide scenarios considered in application of the model, the directional dependency is shown to change the accumulated plastic strain profile in the pipe.